Compound hydraulic compressor



March 14, 1944. M.v.-GRovEs 2,343,901

COMPOUND HYDRAULIC COMPRESSOR Filed Oct. 24, 1942 l3 Sheets-Sheet 2 Afyz,

INVENTOR. 1W): @rnv VVG/ 20 VES.

ATTORNEYS March '14, 1944'. y M, v GRQVES 2,343,901

COMPOUND HYDRAULIC COMPRE-SSOR Filed Oct. 24,1942 3 Sheets-Sheet 3 @s .A ff 62 63\ l INVENToR.

MA Riv/v VGRO v5.5. Y

ATTORNEYS Parental Mu. 14, 1944 UNrrso STATE 2,343,901 COMPOUND HYDRAULIC COMPRESSOR ooklyn, N. Y., assigner of Martin V. Groves, Br

one-half to Arthur Wi Ryde, Bayside,l N. Y. y Application October 24, 1942, -Serial No. 463,165 14 Claims. (Cl. Gil-54.6)

My invention relates to compound hydraulicI brake compressors or the like, and more particu- -larly to a valve structure for'controlling the operation-of said compressor.

This application is a continuation in part of my copending applications Serial No. 366,333, led November 20, 1940, for Compound hydraulic brake compressor and Serial No. 436,584, tiled March 28, 1942, for Hydraulic actuating mechanism."

In structures of this character, the operation comprises in general two stages; the rst stage representing the lowpressure stage an ond stage the high pressure stage. In passing from one stage to the other, the operation is controlled by a high pressure or unloading valve which comes into operation at a predetermined.

pressure. It is. desirable in such structures to have this valve operate in such a way that the carry-over" from one stage to the' other be eiiected with a smooth action so that the change from simple to compound action may be brought about without any noticeable surge in the system. This is particularly important where the compressor is utilized to deliver an ultimate relatively high pressure.

' Additionally, in compressors of the type disclosed in said copending applications, the valve serves as 'a hydraulic coupling between lthe primary and secondary pistons causing them to move togetheras one -unit during the iirst or low pressure stage and permitting relative move- .ment between said pistons during the second or high pressure stageyand in such a structure, it is likewise desirable that the coupling and uncoupling of the two pistons be effected smoothly and without appreciable Jerk.

An object of the present invention is to provide a high pressure or unloading valve structure providing a smooth change-over from low pressure to high pressure.-

so the pressure valve open.

Another object oi the invention is to provide a valve structure which responds out undue Jerk or surge.

Another object of the invention mechanism permitting rocking" .rapid actuating impulses sure.

A further 4object o a compound compressor pressure valve mechanism .in a priming valve.

Further objects tion will more fully appear 4from description takin in connectie quickly Withis to provide or successive unit comprising such a and advantages of the invenwithout losing prestheinvention is fo'provide simpliiied high pressure elates more particularly combination with ifollowingwith the aell vtherein iofr reciprocal movement is .primary pisvto show the full and complete ide and Arthur Hullreferredv embodiments of the in the appended claims.

Referring to the drawings: I Fig. 1 is a longitudinal sectional view illustrating the compressor unit embodying the invention;

Fig. 2 is a somewhat enlarged View of certain parts of Fig. l showing the pressure and priming valve structure, with both valves closed;

. Fig. 3 is a view similar pressure valve commencing to open;

Fig. 4 is a view similar to Fig. 2 but showing .the pressure valve fully open;

Fig. 5 is a view the priming valve open in closed position;

Fig. 6 is an enlarged longitudinal sectional `view showing a modiedstructure of pressure and priming valve, with both valves in closed position;

Fig. 7 is a with the pressure valve Fig. 6 but showing iming valve view-similar to with the pr in closed position;l

Fig. 8 is a view similar to Fig. 6 but showing the priming valve open with the pressure valve in closedposition;

Fig. 9 is a longitudinal cross-sectional view oi a portion of a compressor unit, showing a somewhatmodied form oi structure;

Fig. 10 is a longitudinal cross-sectional view of a portion of the compressor unit showing a further modified form oi structure; and

Fig. 11 is an enlarged longitudinal crosssectional viewv showing a modified and somewhat valve structure. invention r arrangement, only "Details oi the invention described the subject matve referred the parts. but not claimed herein form terof saidcopending'applications a to. l

Referrin mary cylinder tong. 1, a. prig more and positioned is -designatedas i.

drawings which show, by way oi?v novel features,

ventions will be morey particularly pointed out l,

to Fig. 2 but with the similar to Fig. 2 but showing ture of the tn 2fprovlded with`r spaced lng sealing cups 3 and 4.

what reduced in diameter intermediate the cups 3 and 4 to provide an annular chamber 5 which is in constant communication with they reservoir 6 through a port 1. The reservoir 6 is provided with a further port 8 which with the space 9 provided in the. cylinder I forward of the head 3 when the piston is in retracted position, as indicated in 'the drawings. The space 9 provides a pressure chamber adapted .'to Ibe placed in communication, as by an outpressure line, such as a brake system, and egress and ingress is controlled by suitable check valve mechanism designated in its entirety as II. A plurality of ports I2 provide passage of uld from the annular chamber to the pressure chamber 9 [to provide for bleeding the system, and the sealing cup 3 prevents reverse passage of :the fluid from the chamber 9 into the chamber 5. The primary piston 2 is urged rearwardly by a. retractile spring I3.

'Ilie primary piston 2 is provided with an axial apart heads compris- The piston is somecylinder .I, chamber' 20, which for purposes of convenience will be referred to as the primary chamber. Between this cham- `bers and the space I8, there is provided a checkvalve designated vas 2|, so constructed and arto be manually operated., A sealing cup 21 is in sealing engagement between the secondary piston and the bore 22.

Referring more particularly to Figs. 25, lnclusive: The bore I5' in the secondary piston cup are urged against the seat 29 a relatively light priming valve spring 33 which by means of is in communication 'first or low pressure stage.

recess provided in a priming is seated within a dispOsed within valve spring retainer washer 34 the b'ore I5 and seatedagainst 29. .'I'lie washer 34 also serves lower end of thes'econdary piston retractile spring I1, which being stiffer than the spring 33 maintainsI the washer 34 against; its seat; suiicient clearance being provided beneath the washer 34 to permit the opening of the valve 30-3I, against the action of the spring 33, to the open position shown in Fig. 5. lThe washer 34 is provided with a. central opening so as not .'to obstruct passage of iluid from the secondary cylinder I4 and bore l5 to the bore 35.

The valve body 32 is provided with an axial bore 35 and with one or more outwardly radially extending passages 36; the bore 35 providing the inlet port, and the passages 36 The body 32 rearwardly of the priming valve head 3| is of less diameter .than that of `the bore 28, to thereby provide an annular space or passage.

The body 32 is also provided with a cylinder 31 in communication with the bore 35 and having its rear end opening into the chamber 24 (Fig. 1). A valve portion or plunger 33 is slidably disposed in the bore 35, and in the position shown in Fig. 2, serves to close the passages 36 from communication with the bore 35 at its intake or high pressure end where it is exposed to the pressure from the secondary chamber I4. The valve enlarged head 39 disposed within the cylinder 31, and a relief groove 40 is preferably provided between the plunger 38 and head 39. A sealing cup 4I, with its flange turned forwardly, is positioned within the cylinder 31 with its forward face resting upon the enlarged head 39 and with its rear face engaging the spring Iretainer cup 42 within which is seated the forward end of the spring 43 whose rear end is conned by a washer 44, which is held in place by the inturned end of the body 32; .the washer 44 being provided with an enlarged opening so as not to interfere with communication between the cylinder 31 and the space or chamber 24 provided with a concentric peripheral bead on its forward face within which is seated the enlarged head 39, and with a corresponding bead on its rear face seated in a cooperating grove formed in the cup 42 so as to'maintain proper alignment betweenl the parts and serving the additional funtion of conning the sealing cup (which ls preferably made of relatively elastic material, such as rubber). The sealing cup 4I and spring retaining cup 42 are provided with registering When it is desired to provide pressure in the line attached to the opening I0, the device is actuated by applying pressure to the end 26 of the secondary piston. At this time, the priming valve 30-3I is seated against its seat 29 (Fig. 2) and the high pressure valve 35-38 is closed, thereby trapping the fluid in the chamber I4-I5. This acts as a uid coupling between the pistons 2 and I5, causing them to move as one unit during the As the piston 2 is moved forward, the port 8 (Fig. 1) is closed, and

vwhen a predetermined pressure is developed in the system by the forward movement of the pisplunger 38 is provided with an (Fig. 1). The sealing cup 4I is4 2, a corresponding pressure is imposed in (Fig. 2') to the position ings in the the `valve plunger rate of ilow, the' movement of v 33 to open position is damped, thus preventing inclusive, the cup this lpermits uid from space 24, through the port 23,

'sirable that the high pressure valve cylinder I4 and bore`- |l som to actuate the valve 33, whereupon the high 33 is moved rearwardly from the initial position shown in Fig. 3, at which time the relief groove 43 is moved out of communication with the passages 33 and upon further movement of the valve plunger 33 and enlarged head 33, the' sealing cup 4I is moved rearwardly against the force of spring 43. This creates a suction forwardly of thewup 4I, i. e., a

difference in pressure between the chamber formed forwardly of the cup (within which the head 33 ispositioned) and the pressure on the .rear side or the cup. This difference in pressure fluid to ow through the aligned opencups 4I and 42; the rate of flow being regulated by the strength of the spring 43, the diameter ofthe plunger head 33 andthe t of 33 in the bore 35. The ilt of the plunger head 33 in the bore 35 is preferably a fairly close sliding tit, and therefore for a given pressure exerted on the forward end of the valve portion 33C the rate of flow from the rear side to causes theV `the front side of the cup 4-I is controlled by proper calibration of spring 43 and the diameter of head 39. By providing such a predetermined the valve plunger an immediate snapping open of the highpressure valve and avoiding the rapidity of unloading which would result in an undesirable surge or too rapid change-over fromthe low pressure to the high pressure stage. jacent faces of the head 33 and sealing cup 4I is greatly exaggerated in Fig. 3 in order to more clearly show the space through which the iluid passes at uns stage of operation. It is noted that sufficiently semble, aum wm if the cup 4I is made pass from the chamber past the periphery of the cup 4I into the chamber forwardly of said cup. However, in the embodiment of Figs. 2-5

4I is-so formed and disposed as to aiord no appreciable passage of uid thereby; chief reliance being made for the'passage of fluid by means of aligned openings formed in the cup 4I and cooperating backing cup 42. In other embodiments to be described following, the flexibility of a cup comparable to 4I is relied upon pressure valve plunger actuating pressure from the of fluid through the -plunger 33 to move The space between the adjerky operation due to as the chief means for passage of the iluid into l the locking chamber. Applicants experience has indicated that a somewhat more accurate calibration has been obtained by' utilizing the passages through'the cup and backing member for calibration purposes; although he has successfully usedthe alternative structure, as well as a combination (of the two. I

Upon continued operation, the valve plunger 33 is moved to the position indicated in Fig. 4, at which time the bore 33 has been placed in complete communication with the passages 33 and the secondary cylinder the bore 23, into the and thence into the chamber 20 which has now been closed by the closing of valve 2| permitted by the forward movement of 'the secondary piston I5. Continued application of actuating pressure to the to pass rearwardly through valve head 46 carrying suitably It will thus be seen and the rate of .'ow of the fluid until the actuating pressure on the compressor is released, and even upon release, the valve should not close immediately since this will produce surge or Jerky operation. With the parts as shown in Fig. 4, fluid is trapped in the chamber on the forward side of the sealing cup 4I and the plunger head 33 is locked in open position by the pressure exerted on the forward face of the head 33, thus preventing the high pressure valve from closing until the release of the iiuid thus trapped. regardless of:V the pressure exerted by the spring 43 and the hydraulic pressure in the chamber 24. However, when the pressure in the secondary cylinder I4, which is exerted through the bore 35 upon the plunger 33, is relieved by removing part 23, the pressure openings in the cups 4I'42 is exerted upon the head 33 thus Vpushing the head away from the cup 4I, thereby breaking down the lock chamber seal and permitting the forwardly to the position shown in Fig. 3. .Upon further movement of the relief 'recess 40 places the locked to assure the prompt and full closing of the high pressure valve by freely venting the locked chamberpassage. After the high pressure valve has thus been closed, and upon the rearward movement of the parts' under the influence of retractile springs I3 and I1, the rearward movement of the small piston I5 lowers the pressure in its cylinder i4, thereby opening 4the priming valve 313-3!l to the position shown in Fig. 5 and permitting the flow of iluid from the chamber 2li through the port 23, through the chamber 24, through the bore 23 through the open priming valve into the bore I5 and cylinder I4.

that the opening and closing ofthe high pressure valve is damped by the fluid pressure and in its open position is held open by the duid pressurel even though they pressure in the compressor is sively raised and lowered, without permitting the too rapid opening and closing of the high pressure valve. In this damp-v inglaction,v the head 33 in cooperation with the sealing cup 4I forms providing means for controlling the ilow'of the fluid from one side of l may be flxed at any predetermined value to eiect the desired degree of damping Referring more particularly to Figs. 6, 7 and 8,

a somewhat modified form of' valve structure is shown in which the valve body is designated as 45 and its forward end is provided with a priming a sealing ring 41 adapted to engage, when in closed position. a cooperating valve seat 43. In

this embodiment, the priming valve is held in closed position by the secondary piston retractile spring I1: and it is noted in this connection that the use of the common spring for the priming u valve and retraction of the secondary piston does as nexible adjustment and operanot permit of -tionas the preferred-'form previously described end 23 of the small piston Il causes it to move' forward within the' cylinder I4 passing the relin which epl'ai Sprlnlis used for the,priming valve. The body 43 is 'provided with an axial bore 43 in which is slidably disposed va valve plunger Il serving to open and'close one orfmjore passages, such as 3i.' which are on their outer ends with lan annular space 32 which is in communication with the chamber 2l (Fig. l) in the manner and for the purposes previously described in connection with the valve rockedf i, e., succesin effect a. damping piston the piston tothe other:

seomed thereto in. communication mechanism disclosed in Fig. l..4

beneath the piston takes place the chamber v52 and past the valve wlfiich is formed a low valve 63 is provided The valve plunger 5| lcarries an enlarged head 53 which is disposed in a cylinder 54 provided in the body 45 and the rear face of the head 53 engages the front face of a sealing cup 55 which is engaged on its rear face by a spring retaining cup 56 receiving the forward end of a compression spring 51 whose rear end is restrained by means of a retaining washer 58 suitably secured to the outer end of the body 45; and the washer is provided with lan axial opening to permit free access of fluid between the cylinder 54 to the rear of the cup 55 and the chamber (Fig. 1). In the operation of this embodiment, the passage of fluid from the rear compartment of cylinder 54l past the piston, comprising the head 53 and cup 55, is largely effected by leakage past the peripheral ange of the cup 55; while the passage of vuid rearwardly from between the head 53 and the cup 55 and thence rearwardly through the aligned axial openings provided in the cups 55 and 56. A further distinction is that in this embodiment no relief groove is provided in the stem o f the plunger 50 intermediate its forward end and the head 53and accordingly theultimate closing of a valve of this embodiment is not expedited to the extent of the valve previously described in connection with Figs. 1 to 5, inclusive. Fig. 7 shows the high pressure valve in open position, vat which time the locked chamber between the forward side of the piston and the forward endA of cylinder 54 is lled with fluid under pressure. In`Fig. 8, the parts are shown in the cycle of operation previously described in connection vwith Fig. 1 when the high pressure valve is closed and the` priming valve is moved forwardly from its seat to permit the free passage of iiuid from the primary chamber to the second'- ary chamber. For example, during this operation, the valve 2| is closed and the uid in chamber 20 to the rear of the large piston 4 escapes through the annular passage 22, the ports 23, 46-48 into` the primary cylinder I4; the valve 46 being urged forwardly to its open position (Fig. 8) against the spring I 1 by the greater force exerted by the spring I3 which serves to retract the large piston. As soon as the large piston is moved rearwardly a sufficient piston I6, the valve 2| is opened, thereby venting whose rear end is seated inthe recess formed in the valve body 1| provided with a priming valve head in which is carried `a suitable priming valve sealing ring, 12 of as rubber, for cooperative engagement with the priming valveseat- 13. 'I'he valve body 1| is provided with an axial bore 14 and with one or .more outwardly extending passages, such as 15, communicating with an annular passage 16 which is in communication with a chamber 11 which is placed in communication with the primary chamber 62 by means of an axial bore 18 and one or more outwardly rextending passages 19. A valve plunger 80 is disposed within the bore 14 for the purposes previously described. and carries an enlarged head 8| disposed within the cylinder 11 and whose rear face is engaged by a sealing cup 82 carrying on its forward face a concentric bead engaging a cooperative groove in the head 8|. The cup 82 and head 8|, as well as the valve plunger 80, are urged forwardly by means 0f a spring 83 suitably retained in position by means of a washer 84 in thegeneral manner previously described. 'Ihe'operation of this embodiment is quite similar to the embodiment previously described in connection with Figs. 1-5, inclusive, and therefore will not be set forth in further detail. It is noted, however, that in this embodiment, cup 82 is so formed and disposed that fluid from the rear thereof passes by the periphery of the cup when the same Iis urged lrearwardly against the spring 8.3 by means of the head 8|; the concentric bead on the cup 82, seated in a cooperating groove in the head 8|', serving to center the head on the cup vand the relatively thin peripheral flange of the cup 82 providing the necessary flexibility to permit' the passage of fluid thereby under the differential of pressure between the rear and front of said cup. In practice, this distance relative to the small `v the -chamber 20 through the open valve 2| and past the sealing ring of piston I6 and into the cylinder I4'.

r Referring more particularly to Fig.- 9, a somewhat modied form of structure is disclosed in which the large cylinder is designated as 59 in which is provided a large piston 60 whose rear head comprises a sealing cup 6| to theA rear of responding to the chamber 20 of Fig. l. A checkfor opening and closing this chamber by way of ports, such as 64, corresponding to the ports |9 of Fig. l. ary' cylinder is designated as 65 and contains a secondary piston 66 provided with a head'comprlsing a sealing cup 61.- -A spring retainer 68 is seated on a forwardly extending sleeve integrally formed with the secondary piston 66l and sup. ports on `its forward face a retractile spring I9 and onv its rear face a priming valve spring 1l spring I1 then closes the valve a priming valve sealing cup porting ring 93.

pressure chamber 62, cor- A small or secondlbore |00 and vannular space 96 as in the arrangement has been found to give satisfactory result. i

The modification shown in Fig. l0 is quite similar in general principles to that previously described in connection with Figs. 1 and 9, and therefore the parts will only be designated in general except as to certain portions of the valve structure which will .be described in somewhat more detail. In this embodiment, the large cylinder is designated as 85, the large piston as 86,

the small cylinder as 81, and the small piston asl 88. The retractile spring for the small piston is designated as 89 and is retained at its rear end in a spring cup l90 which is seated in the forward end of a bore supplied in the secondary piston 88; and the rear end of the cup serves to restrain a priming valve spring 9| whose rear end engages 92 mounted on a sup- Unlike the preceding embodiments, in this structure the priming valve sealing cup 92 is movable with respect to thevalve body 94, on the forward end of which is formed the priming valve seat 95, and the valve body 94 is rigidly secured to valve body 94 ranged in the that in this is in general constructed and armanner previously described except embodiment an annular space 96 vcommunicates with thel primary compression 96 into the valve cylinder 99, through an axial outwardly through one or more passages |0|; inst'eadofpassing directly from the previous embodiment.

A further modification resides inthe provision of asealinglcup |02 which is formedwith forwardly suitable elastic material, such f the secondary. piston 88. 'Ilie ycalibration spring |05.

`cylinder on 'the and rearwardly extending flanges, the forward flange surrounding the valve head |03 and the rear flangesurrounding a reduced portion of a cup |04, whose rear face is recessed to receive a The double iiange arrangement of the -cup |02 assures somewhat greater rigidityagainst deformation than the embodiment of Figs. l-5, inclusive, and it has been found that in dealing with relatively high pressures, the calibration of this type of structure gives entire satisfaction; the central opening through the cup |02 being -relied upon for passage of the desired damping action. 'I'he valve head |03 is integral with a valve plunger having a sliding it in the high pressure intake bore |01, and a relief groove |00 is provided as in the previous embodiments of Figs. 1-5, inclusive, and Fig. 9. The cycle of operation and function of this embodiment is in general similar to that previously described in connectionwith Fig. 1, and therefore will not be further elaborated upon.

Instead of utilizing a damping piston comprising the enlarged head of the high pressure valve in combination with a sealing cup, as in the previously described embodiments, Fig. 11 illustrates a modified form in which the sealing cup is eliminated. In the embodiment of this modiiication shown in Fig. ll, the structure is quite similarto that of Fig. and to facilitate description, corresponding parts are designated by the same respective numerals with an addedv prime suflix. The valvebody 94' is the same as in Fig. 10 and is similarly disposed. The high pressure valve head |03' is increased in diameter so as to serve as a piston without the sealing cup as heretoforede-` scribed. This piston |03' is of such diameter as to provide for a restricted-passage of fluid between its periphery and the cylinder walls of the cylinder 99'. The valve plunger |06' has a sliding fit in the bore |01 and a relief groove |08' is provided, all as heretofore described. In a brake compressor-Which unloads at approximately 150 pounds and whose high pressure stage builds up to approximately 2000 pounds, I have found that with the valve cylinder 90' having a diameter of approximately 'l/", the piston |03 having a` clearance of `about .005" has proven quite satisfactory where the bore |01 has 'a diameter of about V8" and the valve plunger |06' has a sliding clearance thereinof about .0002".

Having thus described my invention with particularity with reference to the preferred embodiment of the same, and-having referred to some y 0f the possible modifications thereof, it will be obvious to those skilled in the art, after understanding my invention, that other changes and modiflcatoins may be made therein without dethe uid to the left of the cup to give low pressure side and a parting r.from thevspirit and scope of the inven'-- tion, and I aim in the appended claims to cover such changes and modifications as 'are within..

the scope of the invention.

-WnatIclaimisz y l. Arx-unloading valve for interconnecting a' v. low pressure side and a high pressure side in` a compound hydraulic actuator, comprising means l of communication between said low pressure side and said high 'pressure side,A a valve portion controlling the ilowof' uid through said means oi' communication, resilient means for urging said valve portion to closedposition. a piston movableA with said valve portion, and a cylinderl in which said piston is disposed and providing with the under side of said piston a fluid chamber, said other side or said piston being 1n piston is disposed and providing with side of said piston a iluid chambensaid cylinder,

low pressure side. said being movable against communication with said valve portion and piston on said high pressure side to open said means of communication, means to pass uid in either direction between said iiuid chamber and the low pressure side of said piston, whereby upon the opening of said uid chamber from the low. pressure side of said piston to hold the piston `loutwardly against said resilient means and the valve is held in open position until saidv predetermined lpressure on said high pressure side is reduced, whereupon fluid is passed from said chamber to said low pressure side of said piston andthe valve is returned to closed position.

2. An unloading valve for interconnecting a high'pressure side in a comprising means pressure side compound hydraulic actuator, of communication between said low and said high pressure side, a valve portion controlling the iiow of fluid through said means of communication, resilient means for urging said valve portion to closed position, apiston movable with said valve portion, a cylinder in which said the under on the other side of said piston being in communication with said 'low pressure side, said valve portion and piston being movable against said resilient means by predetermined pressure on said high pressure side to open said means of communication, said piston being constructed/and arranged so as to pass fluid from thel outer side of said piston into said uid chamber upon the opening of said valve to hold the piston outwardly against said resilient means whereby the valve is held in open position until said predetermined pressure on said high pressure side is reduced, and means disposed forwardly of said valve piston for venting said fluid chamber.

3. A valve structure comprising a valve body having a high pressure inlet bore provided with an outlet port, a valve movably disposed in said valve, a valve piston said valve to closed position spring means urging in said cylinder, .said

and said piston forwardly piston defining a rear compartment'and a front I compartment which constitutes a lfluid chamber, .means for providing a restricted fluid path from said rear compartment to said `fluid chamber during the rearward movement of said piston and from said fluid chamber to said rear compartment upon the forward movement of said piston.

and means for passing iiuid outwardly from said l fluid chamber exteriorly of said rear compartf ment.

4. In a compound hydraulic master cylinder I having a primary chamber and a' secondary chamber, a valve for interconnecting said cham? bers comprising a cylinder body having a large bore in communication with said primary chamber and a small bore extending from said large bore and in communication with said secondary chamber and a port e tending outwardly from Q saidsmall bore and in communication withsaid primary chamber, a valve plunger having a' large head in said large bore and a small'head in said smallb'ore, resilient means urih said plunger inwardly to close said port to fluid passage from said secondary chamber through said small bore. said plungerv being movable outwardly against valve uid is passed into said v ony ,saidl movable with said valve and disposed within a cylinder provided'in said body.

y secondary chamber,

. thereof and i to Y pass sudabiy mounted ink a flexible valve pressure exerted on-said ,smallhead -from said large' bore and the outer Iaceof said large head constructed and arranged to create suction behind said head upon the outward movement fluid inwardly and 4beneath said large head upon itsmovement outwardly to th'eby hold said valve in open position during the application of said predetermined pressure, and vent means comprising said sealing means and said large head to control the passage of uid outwardly from beneath said head to release said valve when said predetermined pressure is reduced.

5. An unloading valve for interconnecting a low pressure side and a high pressure side in a compound hydraulic actuator, comprising means oi' communication between said low pressure side and said highpressure side, a valve portion coptrolling the i'iow of iiuid through said means of communication, resilient-means for urging said valve portion to closed position, a piston movable with said valve which said piston is disposed and providing with the under side of said piston a holding chamber, said cylinder on the other side of. said piston4 being in `communication with said low pressure` sealing meansengaging said cup and flange, locking the valve open until the 'iiuid pressure fa permitting said resilient means to close said valve with the uid in said cup escaping through said openings.

Y 8. A valve structure comprising a valve body having a high pressure inlet bore provided with an outlet port, a valve movably disposed in said bore to open and close said port responsive to portion, and a cylinder in side, said valve portion and piston being movable against said resilient means by predetermined pressure'on said high pressure side to open said means oi communication, means"to pass uid in either direction between said iluid chamber andl the low pressure side of said piston, whereby upon the opening of said valve fluid is passed into said fluid chamber'from the low pressure side o1' said piston to hold the piston outwardly against said resilient means andthe valve is held in open position until said predetermined pressure on said high pressure side is reduced, whereupon iuid is passed from said chamber to said low pressure side of said piston andsaid valve is returned to closed position. 'l

6. In a compound hydraulic brake compressor, a cylindrical body having fluid passages, a high pressure lvalvefmounted in said body and' conrollingsaid passages and having a flange portion of smaller diameter than the internal diameter ofsaid cylindrical body, a ilexible valve cup said cylindrical bodyand having a central opening engaging said flange portion, a piston open until the fluid .pressure falls, permitting said resilient means to close said valve with the fluid in said cup escaping through said openings.

7. In av compound hydraulic brake compressor. a cylindrical body having fuid4 passages, a high pressure `valve mounted in said body and controlling said passages and having a flange body,

cup slidably mounted in said cylindrical body and having a central opening engaging saidk ilange portion, a piston engaging said cup and having an opening aligned with said cenresilientmean's urging said piston and valve cup and high pressure lvalve in one directionv for urging the high pressure valve closed, Vwhereby when iluid pressure forces said high pressurevalveopen, iiuid enters past Said `said valve,

predetermined fluid pressure exerted on said valve, a valve piston movable with said valve and disposed within a cylinder provided in said body, spring means urging said valve to closed position and said piston forwardly in said cylinder, and means including said spring means and said cylinder and said piston vfor hydraulically holding said valve in open position and damping its opening and closing responsive to iluid pressure exerted on said valve whereby said valve is closed only when there is a deiinite pressure diilerential acting on the valve in the direction of said spring means. i

9. A valve structure comprising a valve body having a high pressure inlet bore provided with an outlet port, a valve movably disposed in said bore to open andclose said port responsive to predetermined pressure exerted onjsaid valve. a valve piston movable with said valve and disposed within a cylinder provided in said body, spring means urging said valve to closed position and said piston forwardly in said cylinder, means including said spring means and said. cylinder and said piston for hydraulically holding said valve in open position and damping its opening and closing responsive to iluid lpressure exerted on said valve, whereby said valve is closed only when there is a definite the valve in the direction of said spring means a second valve body having an opening concentric seat to closed position and yieldable in the opposite direction to thereby provide a one-way priming valve. y

10. A valve structure comprising a valve body having a high pressure inlet bore provided with an outlet port, a valve movably disposed in said bore to open and close said port responsive to predetermined pressure exerted on said valve. an enlarged head integral with said valve and disposed within a cylinder provided in said body, sealing means engaging the walls o1' said cylinder, spring means urging said sealing means against said head and urging said head to closed position, and means including said head and said sealing means and said spring means and said cylinder for hydraulically holding said valve 1n open position and damping its opening and clos' combination of, a valve structure comprising a valve body having a high pressure inlet bore provided with an outlet port, a valve movably disposed in said bore to open andclose said' port responsive to' predetermined pressure exerted on a valve piston movable with said valve and disposed within a cylinder provided in said L... ...a e

pressure diierential acting on urging said piston outwardly,` the body, spring-means urging said valve to closed position and said piston forwardly in said cylin.

der, means including said spring means and said cylinder and said piston for hydraulically holding said valve in open position and damping its opening and closing responsive to fluid pressure exerted on said valve, a second valve body having an opening concentric with and of larger diame-l cal body whose rear end is in communication with said primary chamber and whose forward end is provided with an axial bore in communication with said secondary chamber, a sealing cup movably disposed within said cylindrical body dening a-rear, compartment and a front compartment, resilient means urging said cup toward the forward end of said cylindrical body,l a valve plunger extending into said axial bore with its forward end exposed to said secondary chamber fluid pressure and provided with a head of larger diameter than said bore positioned within said front compartment and urged into forward position by said cup under the influence of said resilient means, a port extending outwardly from said bore and in communication with said primarychamber, said port being closed to saidsecondary chamber by said plunger when in its forward position, ysaid cup and said plunger head jointly providing means for controlling the passage'of fluid between said rear and forward compartments.

13. In a compound hydraulic brake compressor having a primary chamber and a secondary chamber, a valve for controlling fluid passage beetween said chambers and comprising, a cylindrical body whose rear end is in communication with said primary chamber and whose forward end is provided with an axial bore in communication with said secondary chamber, a sealing cup movably disposed within said cylindrical body denning arear compartment and a front compartment, resilient 'means urging said cup towardthe forward end vof said cylindrical body, avalve forward end exposed to said secondary chamber -fluid pressure and provided with a head of larger diameter thansaid bore positioned'within said front compartment and urged into forward posi tion by said cup under the influence of said .resilient means, a port extending outwardly from said bore and in communication with said. primary chamber, said portbeing closed to said secondary chamber by said plunger when in its forward position, said cup and'said plunger head jointly providing means for controlling the passage of fluid between said rear and forward compartments, said valve plunger intermediate its forward end and head being of reduced diameter providing a relief passage from said rear compartment to said port when said plunger appreaches the forward end lof its stroke.

14. In a compound hydraulic brake compressor having a primary chamber and a secondary chamber, a combined primingvand high pressure valve for controlling iiuid ,passage between said chambers and comprising, a cylindrical body whose rearend is in communication with said primary chamber and whose forward end is provided with a high pressure valve bore in com--V munication with said secondary chamber, a sealing cup movably disposed within said cylindrical body defining a rear compartment 4and a front Qcompartment, resilient means urging said cup toward thel forward end of said cylindrical body,

3o a high pressure valve, plunger extending into said bore with its forward end exposed to fluid pressure in saidsecondary chamber and provided with a head of largerdiameter'than said bore positioned within said front compartment, said valve plunger being urged into forward position byv said cup under the influence vof said resilient 4means and beingy movable rearwardly against said resilient means by, a pre'deterniined'high pressure in said secondary chamber, port means 40 extending outwardly from said bore and in communication with said primary chamber. said port means being positioned to be closed to-said secondary chamber by said plunger when in its forward position and to be opened .to said secondary chamber when said plunger is in a rearward position, said cup and said plunger head jointly '-providing means for controlling thepessage of fluid between said rear and forward compartments, a concentric priming valve seat of larger diameter than said-high pressure valve bore dis- Y posed forwardly of said port means, `a priming valve secured to said cyllndrlcalbody, and resilient means for `yieldably holding said priming valve against its seat.

plunger extending into said axial bore with its naam v. GaovEs. 

